hey i have a silly question. is there any time when you wouldnt count a neutral as current carrying conductor in a derate situation. example. i have 3 20A,125, 3wire single phase twistlocks (each with own neutral) and one 20A 120/208, 5 wire 3phase twistlock all in a single 3/4 emt home run. so does that makes 9 or ten current carrying conductors, do i count the neutral in the 3phase 5wire 20A or do i disregard that conductor since its 3phase? had this question at work and just trying to clarify for own benefit.oh its all THHN awg.
derating ?
- Thread starter cisco28
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Re: derating ?
Assuming linear loads, if you put all the 125 v twist locks on different phases (i.e. ABC) and used one neutral, it would not be current carrying and would not be counted.
The neutral for the 5 wire receptacle most likely would not need to be counted, once again, this is dependant on the load.
Roger
[ May 19, 2005, 08:41 PM: Message edited by: roger ]
Assuming linear loads, if you put all the 125 v twist locks on different phases (i.e. ABC) and used one neutral, it would not be current carrying and would not be counted.
The neutral for the 5 wire receptacle most likely would not need to be counted, once again, this is dependant on the load.
Roger
[ May 19, 2005, 08:41 PM: Message edited by: roger ]
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- New Jersey
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Re: derating ?
As Roger said, if the 5 wire circuit were for a Linear Load than the netural would not count, so you would have 9 current carrying conductors.
As Roger said, if the 5 wire circuit were for a Linear Load than the netural would not count, so you would have 9 current carrying conductors.
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- New Jersey
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- Journeyman Electrician
Re: derating ?
The neutrals in the 2 wire circuits are counted, the neutral in the 5 wire isn't if the circuit is linear. This means that the 5 wire circuit does not contain a non-linear load which is caused by triplen harmonics. Harmonics become additive in the neutral due to a distortion in the sine wave, so the neutral will carry current up to 1.73 times the phase current. Therefore circuits with non-linear loads must have their neutral counted as a current carrying conductor.
[ May 19, 2005, 10:53 PM: Message edited by: infinity ]
The neutrals in the 2 wire circuits are counted, the neutral in the 5 wire isn't if the circuit is linear. This means that the 5 wire circuit does not contain a non-linear load which is caused by triplen harmonics. Harmonics become additive in the neutral due to a distortion in the sine wave, so the neutral will carry current up to 1.73 times the phase current. Therefore circuits with non-linear loads must have their neutral counted as a current carrying conductor.
[ May 19, 2005, 10:53 PM: Message edited by: infinity ]
hurk27
Senior Member
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- Portage, Indiana NEC: 2008
Re: derating ?
It has nothing to do with a 5th wire. It has to do with where the major portion of the loads are non-linear when applying the derating factors required in 310.15 on a three phase 4 wire Y circuit.
[ May 20, 2005, 12:27 AM: Message edited by: hurk27 ]
It has nothing to do with a 5th wire. It has to do with where the major portion of the loads are non-linear when applying the derating factors required in 310.15 on a three phase 4 wire Y circuit.
Edit to ad that non-linear loads are electronic ballast, equipment with switching power supply's, or any load that switch's on and off at a higher frequency rate than the supply's 60hz.
[ May 20, 2005, 12:27 AM: Message edited by: hurk27 ]
LarryFine
Master Electrician Electric Contractor Richmond VA
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Re: derating ?
By "linear", we mean that the voltage and current are mostly in phase, because there is little reactance (capacitance and inductance collectively).
Examples of linear loads would be resistive loads like incandescent lighting and resitance heating. Computers are notoriously non-linear loads.
Probably not, since most switching power supplies operate in the kHz range.
By "linear", we mean that the voltage and current are mostly in phase, because there is little reactance (capacitance and inductance collectively).
Examples of linear loads would be resistive loads like incandescent lighting and resitance heating. Computers are notoriously non-linear loads.
hurk27
Senior Member
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- Portage, Indiana NEC: 2008
Re: derating ?
Check with the manufacture of the breakers to see how much you have to derate the breakers.
Not on the derating issue but it will affect the rating of the breakers.
Check with the manufacture of the breakers to see how much you have to derate the breakers.
Re: derating ?
Wayne is right, you need to talk to a manufacturer and let them tell you what their equipment can do at 400hz, this is what I do on 400hz installations.
Skin effect at elevated hz's can change what we normaly see at 60hz.
For example
Roger
[ May 20, 2005, 09:00 PM: Message edited by: roger ]
Wayne is right, you need to talk to a manufacturer and let them tell you what their equipment can do at 400hz, this is what I do on 400hz installations.
Skin effect at elevated hz's can change what we normaly see at 60hz.
For example
Roger
[ May 20, 2005, 09:00 PM: Message edited by: roger ]
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